Conveyer apparatus and control system therefor



Sept. 14, 1954 c. w. HElL 2,688,932

CONVEYER APPARATUS AND CONTROL SYSTEM THEREFOR Original Filed Nov. 13, 1945 3 Sheets-Sheet 1' 3 Sheets-Sheet 2 C. W. HEIL CONVEYER APPARATUS AND CONTROL SYSTEM THEREFOR Sept. 14, 1954 Original Filed Nov. 13, 1945 Sept. 14, 1954 c. w. HEIL 2,638,932

CONVEYER APPARATUS AND CONTROL SYSTEM THEREFOR Original Filed Nov. 13, 1945 3 Sheets-Sheet 3 fidQ/Zzbiti 6/12/44 at M 4, www g &

Patented Sept. 14, 1954 CONVEYER APPARATUS AND CONTROL SYSTEM THEREFOR Charles W. Heil, Fairfield, Iowa, assignor to The Louden Machinery Company, Fairfield, Iowa, a corporation of Iowa Continuation of abandoned application Serial No. 628,170, November 13, 1945. This application February 2, 1953, Serial No. 334,701

19 Claims. 1

This invention relates to conveyor systems including trackways or guides and conveyors adapted to move thereon, and control means for controlling the stopping and starting of the conveyors as well as the direction of their movement. More particularly, the invention relates to control systems for conveyors running on trunk and branch trackways having different stopping points, wherein any conveyor embodies means within itself to predetermine its course of travel and its stopping point, so that once a conveyor is started on its way and is beyond the immediate control of the operator, it selects the branch trackway it is to run on and it further selects the stopping point on the branch trackway, both as predetermined by the operator, and it is an object of the invention to provide an improved conveyor control system of the character indicated.

This application is a continuation of ,co-pending application Serial No. 628,170 filed November 13, 1945, by the same inventor and which application is now abandoned.

It is a further object of the invention to provide an improved control system for conveyors.

In the copending application Serial No. 603,158, filed July 4, 1945, now abandoned, entitled Conveyor Apparatus and Control System Therefor, and assigned to the same assignee as the present invention, a conveyor control system embodying generating means carried by conveyors moving on a system of trackways and receiver circuits arranged adjacent track switches for cooperation with the generating means to control operation of the track switches together with generating means disposed at stop stations along the trackways and receiver circuits carried by the conveyors for cooperation with the latter generating means to control stopping of the conveyor is disclosed. Such arrangements are bulky, expensive in construction and diflicult of maintenance. Accordingly it is a further object of the invention to provide an improved conveyor control system of the character indicated that is simple in character, inexpensive in construction and efiicient in use.

In carrying out the invention in one form, in conveyor apparatus including a trackway, a conveyor adapted to move along the trackway and a source of electrical energy, the combination comprising one circuit component connected to the source of electrical energy, a second circuit component connected to the source of electrical energy, and means responsive to movement of the conveyor to a predetermined position along the trackway to connect the circuit components to each other, thereby to complete an individual control circuit energized from the source of energy is provided. More particularly, a source of alternating voltage having a predetermined frequency disposed along the trackway, a condenser connected to the source of voltage, a series circuit including a second condenser and an inductance connected to the source of voltage, the condenser and the series circuit when connected forming a circuit resonant to a voltage having the frequency of the source, and means responsive to movement of the conveyor to a predetermined position along the trackway for connecting the condenser and the series circuit to each other thereby to form an individual electric circuit connected to the source of alternating voltage are provided along with control means including a trigger circuit whose functioning is adapted to be initiated by an impulse derived from the resonant circuit at th predetermined position.

For a more complete understanding of the invention, reference should now be had to the accompanying drawings in which:

Figure 1 is a schematic diagram of a conveyor system embodying the invention;

Fig. 2 is an enlarged diagram of a portion of Fig. 1, and a circuit diagram of the conveyor control apparatus associated therewith;

Fig. 3 is an enlarged diagram of another portion of Fig. 1, and a circuit diagram of the conveyor control apparatus associated therewith;

Fig. 4 is a. simplified circuit diagram of the conveyor control apparatus when the conveyor is at one point in its pathway of travel;

Fig. 5 is a simplified circuit diagram similar to Fig. 4 when the conveyor is at another point in its pathway of travel; and

Fig. 6 is an end elevational view of a conveyor shown schematically in Fig. 1.

Referring more particularly to the drawings, the invention is shown embodied in a conveyor system having trunk trackway portions 10, II, and I2, branch trackways l3 and I4, and a conveyor [5 adapted to move thereon. The portions l0, H and I2 of the trunk trackway are shown as forming one end of a rectangular loop having the parallel sides l0 and I2 between which the branch trackways l3 and i4 extend. Thus it is contemplatedthat conveyors beginning on portion H of the trunk trackway will move in the direction of the arrow A onto portion I2 of the trunk trackway and along one of the branch trackway-s l3 or I l in the direction of the arrows to portion II.

ways I3 and I4 have been shown, it will become 3 onto portion I of the trunk trackway and back While only two branch trackapparent as the description proceeds that more branch trackways may be added without departing from the spirit and scope of the invention.

Associated with portion I2 of the trunk trackway and. branch trackways I3 and I4 respectively, are the track switches I6 and I1, each having two positions so that in one position a conveyor moving along the trunk trackway will pass through track switches I6 and II to continue on portion I2 of the trunk trackway. In the other position of track switch I6, a conveyor will move therethrough and onto branch trackway I3. Similarly for track switch I! in its other position, a conveyor moving therethrough will move from por-.

tion I2 of the trunk trackway onto the branch trackway I4. In order to bring conveyors moving on the branch trackways I3 and I4 back to portion II] of the trunk trackway, track switches I8 and I9 are associated respectively with branch trackways I3 and I4. Each of these track switches also has two positions so that in one position of track switch I8 a conveyor moving on branch trackway I3 will pass therethrough and onto portion I9 of the trunk trackway, and in its other position a conveyor moving along portion II) of the trunk trackway will pass therethrough and continue on portion II! of the trunk trackway. The track switch I9 similarly has two positions. Along the branch trackway I3, there are a plurality of stop stations 2|, 22, 23, and 24, and along branch trackway I4 there are also a plurality of stop stations 25, 26, 21, and 28. It is contemplated by the present invention that a conveyor moving along trunk trackway will have its control apparatus predeterminately set by an operator so that either the track switch I6 or II will be operated, and the conveyor will be controlled to stop at one of the stopping stations along branch trackways I3 and I4.

Adapted to move over the trunk and branch 'trackways is a conveyor I which embodies apparatus within itself for controlling its stopping and starting as well as for initiating operation of the'track switches. Referring to Fig. 6 it will be seen that the conveyor I5 includes a U-shaped yoke 34 from which the conveyor proper including the conveyor propulsion motor 35 and control apparatus is supported. At the upper ends of the yoke the wheels 32 and 33 are rotatively mounted for running on the flanges of the trackway, e. g., the trunk trackway II, which may be an I-beam as shown. While only one yoke 34 and associated trolley wheels '32 and 33 are shown, it will be understood that another series of trolley wheels which are longitudinally spaced from those shown may be used as indicated diagrammatically by the trolley wheel 29 of Fig. 1. Also associated with the conveyor are the trolleys 36 and 31 which include respectively the pair of spaced apart trolley wheels or other types of contacts 38 and 39,. and 4| and 42. The trolley wheels 38 and 39 are adapted to run on bus bars, and spaced therefrom so as to run upon the same bus bar is another trolley wheel or contact 43. Similarly, the trolley wheels 4| and 42 are adapted to run on bus bars, and spaced therefrom so as to run upon the same bus bar is a trolley-wheel or contact 44; The trolleys 4| and 42, and the trolleys 38 and 39 supply power to the conveyor propulsion motor 35 and also cooperate with the trolleys 43 and 44 to supply control impulses to the conveyor to.

stop the conveyor and to operate the track switches. The spacing between the trolley wheels 4| and 42, and 38 and 39, the spacing of trolley 43 from trolley 38,, as well as the spacing of trolley 44 from trolley 4|, have, values :which will be indicated subsequently in .thisspecification. Mounted on the conveyor is a control box 45 which contains all of the control apparatus carried by the conveyor necessary to control the conveyor in its movements. The control box contains not only the control for the propulsion motor, but also the control mechanism for stopping the conveyor and determining which of the various branch trackways it is to move on, the four-way push button switch 59 being provided to manually control the conveyor. While one conveyor is shown, as many more as are desired may of course be used.

To supply power to the conveyor for propelling it along the trackways, bus bars 43 and 41 extend along the trunk trackway portions I0, II, and I2, the bus bars '48 and 49 extend along the branch trackway I3, and the bus bars 5| and 52 extend along thebranch trackway I4, suitable bus bar sections also being provided on the track switches I6, I'I, I8, and I9 to supply power to conveyors while moving thereon. The bus bars as described form two conductors of a threewire, three-phase power supply and the various trackways III, II, I2, I3 and I4 form the other conductors thereof, the three-phase system being indicated by the reference characters L1, L2, and L3, of which L3 is the trackway and is grounded at all necessary points as shown. While a three-phase supply system has been shown, and the invention will be described in connection therewith, it will be understood that a single-phase alternating'current supply, or other multiphase supplies may be used. The necessary power is supplied to the conveyor motor by the trolleys 38, 39 and 4| 42 contacting the various bus bars, for example, the bus bars 41 and 46 as shown in Figs; 1 and 2.

As previously pointed out, the track switches I6 and I! have two operative positions, one permitting a conveyor moving along trunk trackway portion II to continue its movement along trunk trackway-portion I2 (through trackway position) and a second position in which the conveyor .moves from the trunk trackway portion I2 onto one of the branch trackways I3 or I4 (curved trackway position) Referring to Fig. 2, it will be seen that the track switch I6 is provided with two trackways 53 and 54and associated bus bars. In the position shown. by'the solid lines,

the straight trackway 53 registers with the trunk trackway portion I2, and a conveyor moving on the trunk-trackway will continue thereon. In the position shown by the broken lines, the curved trackway 54 registers with trunk trackway portion I2 and the branch trackway I3, so that a conveyor moving on .trunktrackway portion I2 is deflected therefrom onto branch trackway I3. To move track switch I5 from one position to the other, a three-phase motor 55 is providedand is adapted to drive a gear 55 which engages a gear rack 51 mounted on the track switch. Power is supplied to motor 55 by means of contactors 58 and 59, the contactor 58 controlling the motor to run in a direction to move track switch I6 so that the curved trackway 54 registers with the trunk trackway portion I2 and the curved trackway |3, whereas contactor 59 controls the motor to run in the reverse direction to move the track. switch to a position where the acaacea straight trackway 53' registers with trunk track'- way portion I2. Contactor 58. includes three pairs.

of. normally open contacts 6|, 62 and 63, all of which are operated by a coil 64, the coil 64 being normallynnenergized and must be continually energized in order to hold the contacts 6|, 62. and 63 closed. Th contactor 59 is substantially identical to contactor 58 and includes three pairs of normally open contacts 65, 66, and 6-1, all .of which are adapted to be operated by a coil 68 which is normally unenergized. In order to hold.

contacts 65, 66, and 6 1 closed, the coil 68 must be continually energized and Whenever either of the coils 64 and 68 are de-energized, the contacts associated respectively therewith open.

To accurately control the final position of track switch I6, the limit switches 69 and H are. associated therewith, the contacts of limit switch 1I being normally closed and being opened by the track switch when trackway 54 registers with the branch trackway I3 and trunk trackway portion I2 to de-energize coil 64,v thereby opening contacts 62 and 53 and stopping motor 55. Correspondingly, the contacts of limit switch 69 are normally open and close when track switch I6 moves toward the curved trackway position.

When track switch I6 moves from the curved trackway position to the through trackway position, the contacts of limit switch 69 are opened, thereby tie-energizing coil 68 to open contacts 65 and 66 and effecting stopping of motor 55 as the track switch I 6 reaches this final position.

The track switch I 1 is provided with astraight and a curved trackway as well as a motor for moving th track switch, and contactors for con- :olling power supply to the motor identical with the corresponding elements of track switch l6, and hence these elements are not illustrated in connection with track switch I1.

The track switches I8 and I9 also as previously indicated have two positions so that conveyors moving along branch trackways I3 and I4 can move therefrom onto trunk trackway portion I9, and conveyors moving on trunk trackway portion Ill can move through on track switches I9 and I8. Referring to Fig. 3, the track switch I8 is provided with av straight trackway 12 and a curved trackway 13, so that in the position shown by the solid lines or straight trackway position trackway 12 registers with trunk trackway portion I I1, and in the position shown dotted or curved trackway position, the trackway 13 registers with branch trackway I3 and trunk trac way portion II]. To move track switch I8 from one position to the other, the three-phase motor 14 is provided and is adapted to drivea gear 15 which engages a rack 16 mounted on this track switch. Power is supplied to motor 14 by means of contactors "I1 and 18, contactor 11 controlling the motor to run in a direction to move the track switch from the straight trackway position to the curved trackway position, i. e., curved trackway 1.3; registers with branch trackway I3 and trunk trackway portion I9, and contactor 18 controlling the motor to operate in the reverse direction for moving the. track switch from the curved trackway position to the straight trackway position, 1. e., trackway 12 registers with trunk trackway portion II].

The contactor 11 is of a well known type having three pairs of normally open contacts 19, 85 and EH adapted to be operated by a normally unenergized coil 82. When coil 82 is energized, the: three pairs of contacts are closed and when the: coil is de-energized. thesev pairs of contacts open; Similarly to. contactor. 11:, the. contactor 6s 18 includes the normally open contacts 83,84, 'a'nd adapted to be closed by. the normally. unenergized coil 90. When the coil is energized, pairs of contacts 83,. 84 and 85- are closed, and

,when coil 9-3 is de-energized these contactsopem To accurately position the track switch I8, limit switches 86 and 61 are associated therewith. The contacts of limit switch 86 are closed when track switch I8 is in the straight or through trackway position, and when track switch I8. moves to the curved trackway position the contacts of limit switch 36 are opened to de-energizecoil 62 thereby opening contacts 80 and BI to effect stopping of motor 14. correspondingly, when tracl: switch I8 is in the curved trackway position, the contacts of. limit switch 81 areclosed, and when track switch moves to the straight trackway or through position, th con tacts of limit switch 81 are opened to tie-energize coil 99, thereby opening contacts 83 and 84 toeffect stopping of motor 14.

Similarly to track switch I8, track switch I9 is provided with corresponding apparatus including a motor for shifting the track switch from one position to the other as well as contactors for supplying power to the motor. Since these elements are similar to those shown for track switch I8 and are similarly controlled, they are not illustrated, v

It being contemplated by the invention that the conveyor I5 embody within itself the necessary mechanism or apparatus to selectively determine which of either of track swtiches I6 and I1 will be operated to determine whether the conveyor moves straight along trunk trackway portion I2 or turns off on to either of the branchtrackways I3 or I4, the control units 68 and 89 which are energized through the influence of conveyors approaching track switches I6 and [-1 are associated respectively therewith. Whenever the control unit 33 is energized, power is supplied to motor 55 to move track switch I6 from the straight trackway position to the curved trackway position, i. e., trackway 54 registers with branch trackway I3 and trunk trackway portion I2 (Fig. 2). The control unit 83 is energized in cooperation with apparatus carried by the conveyor (to be described) through a control section which includes a control conductor 9| spaced between and insulated from bus bar 45 by means of insulators 92 and 93. The control conductor 9! therefore has no energization normally and is energized only when the trolley wheels contact it. This, controlsection is placed in the vicinity of track switch I6, but a suflicient distance away from it so that when the control conductor 9| is contacted by trolley wheel 44 and it is predetermined to do so, the track switch It will be moved to the curved trackway position before the conveyor arrives at the track switch.

Whenever the control unit 89 is energized, the operating motor for track switch I1 has power supplied to it to move this track switch to the curved trackway position- Similarly to control unit 88, control unit 89 is energized through a control section in bus bar 46, the control section including a control conductor. 94 spaced between and insulated. from the bus bar 46 by insulators 95 and 96. Control conductor 94 normally has no energization applied to it and is energized only when the trolley wheels contact it. Whenever trolley wheel 44 contacts control. conductor 94 and it is predetermined to do-so, the control unit 89 will be energizedto effect operation of the track switchu, I111 trackway I3.

branch trackway I3 beyond track switch I6, so

that when trolley wheel 42 contacts control conductor 91, contactor 59 will be energized to supply I power to motor 55 for moving the track switch from the curved to the straight trackway position.

Similarly, a control section including a control conductor IOI spaced between and insulated from the bus bar 5| by insulators I02 and I03 is associated with branch trackway I4 beyond track switch I'I so that when control conductor I| is contacted by trolley wheel 42, the motor associ-,

ated with track switch I! is energized to move this track switch from the curved to the straight trackway position.

After a conveyor has moved along branch trackway I3 and is approaching trunk trackway portion I0, and track switch I8 is in the straight trackway position, it is necessary of course that track switch I8 be moved to the curved trackway position. To accomplish this, the'control section including a control conductor I04, spaced insulators I05 and I06, is associated with branch Whenever the control conductor I04 is contacted by trolley wheel 42, coil 82 of contactor TI is energized thereby to effect power flow to motor I4 for shifting track switch I8 to the curved trackway position. This control section is placed before track switch I8 and a suf ficient distance away from it so that a conveyor moving at its normal rate and contacting the control conductor I04, will allow sufficient time to bring about complete movement of track switch I8. With track switch I8 in the curved trackway position, and a conveyor approaches on trunk trackway portion I0, it is necessary that track switch I8 move from the curved trackway to the through trackway position. For this purpose the control section including the control conductor I0! is spaced between and insulated from the bus bar 46 by insulators I08 and I05. Whenever trolley wheel 42 contacts the control conductor I0'I,

coil 90 of conductor 18 is energized to effect the supply of power to motor I4 for moving track switch I8 from the curved to the straight trackway position. This control section is spaced ahead of track switch I8 a sufficient distance so that a conveyor moving on trunk trackway por-. tion I0, and having its trolley wheel 42 contact control conductor ID'I, will allow sufficient time for the track switch to be completely moved to the proper position before the conveyor enters the track switch. Similarly to track switch I8, the track switch I9 is provided with a control conductor III spaced between and insulated from bus bar 5I by insulators H2 and H3, and a to stop the conveyor at any one of the stop stations 2 I, 22, 23 or 24 on branch trackway I3, or stops 25, 26, 21 and 28 on branch trackway I4. The conveyor is driven by the electric motor 35,

I between and insulated from the bus bar 43 by 8.. which motor is supplied .with power from the associated bus bars, and in order to stop the conveyor the power supply to the motor is interrupted by a suitable switch carried by the conveyor, the switch being operated by a control circuit which is. completed at the stop station and includes apparatus stationed at the stop stations and apparatus carried by the conveyor. Referring more particularly to Fig. 2, it is seen that the stop station 2I comprises a condenser II'I, one terminal of which is connected to a control conductor II6 spaced between and insulated from the bus bar 49 by means of insulators H9 and I20, and the other terminal of which is connected to bus bar 48. Since control conductor H8 is insulated from the bus bar 49, condenser II'I normally has no energization applied to it. The condenser Ill, when conductor H8 is contacted by the trolley wheel 43, completes a circuit with cooperating elements carried by the conveyor to form a control circuit to stop the conveyor. Similarly, stop station 22 comprises a condenser I22, one terminal of which is connected to a'control conductor I23 spaced between and insulated from bus bar 49 by insulators I24 and I25, and the other terminal of which is connected to the bus bar 48. Here also, since control conductor I23 is insulated from bus bar 49, the condenser I29 is normally unenergized, and when the control conductor is contacted by trolley wheel 43, condenser I22 cooperates with elements carried by the conveyor to form a control circuit to stop the conveyor at this stop station. The capacities of condensers Ill and I22 differ from each other whereby the cooperating elements carried by the conveyor may be predeterminately set so that a responsive control circuit will be completed when trolley wheel 43 contacts one of control conductors H8 and I23 and not the other to stop the conveyor. Similarly, stop stations 23 and 24 in branch trackway i3 are provided with condensers having different values of capacitance so as to form control or discriminating circuits'with apparatus carried by the conveyor. The stop station 23 is connected to bus bar 48 and to a control conductor I26 spaced between and insulated from bus bar 49 by means of insulators I21 and I28. Stop station 24 is connected to bus bar 48 and to a control conductor I29 which is spaced between and insulated from bus bar 46 by means of insulators I3I and I32. I

The condensers associated with stop stations 23'and 24 have capacity values differin from each other and from the condensers of stop stations 2| and 22 whereby discriminating control circuits may be formed with cooperating apparatus on the conveyor.

The stop stations 25, 26, 21, and 28 are each provided with condensers having the same value of capacity respectively as the stop stations 2 I, 22, 23, and 24, so that once the branch trackway I4 has been chosen rather than branch trackway I3, the same control apparatus carried by the conveyor may be used to stop the conveyor at stop stations 25, 26, 21, and 28 as is used for stopping the conveyor at stop stations 2|, 22, 23, and 24. The stop station25 is connected to a control conductor I33 spaced between and insulated from bus bar 52 by means of insulators I34 and I35, the stop station 25 also being connected to the bus bar 5|, as shown. Similarly to stop station 25, the stop stations 26, 21, and 28 are connected respectively to control conductors I36, I31, and I38, each of these control conductors being spaced between and insulated from the bus l9 bar 52 as shown. Whenever the control conductors I33, I36, I31, and I38 are connected by the trolley wheel 43, and the control apparatus .carried by the conveyor is set so as to cooperate with one of these control conductors, a control circuit will be formed to stop the conveyor.

The control box 45 carried by the conveyor I includes a propulsion motor controller I39, a track switch selector I40 having positions 1, 2 and 3 (Fig. 1), and a receiver I42. The motor controller I36 is operated to stop and start conveyor propulsion motor 35, the selector I46 cooperates with apparatus associated with control units 88 and 89 to form responsive circuits for operating track switches I6 and I Land the receiver I42 cooperates with the condensers mounted at the various stop stations in order to form responsive circuits to control the stopping of the conveyor at desired points.

In Fig. 2 the circuit elements of the control unit 88 associated with the track switch I6 are shown along with the selector unit I45 mounted on the conveyor in order to more completely describe the operation of track switch I6. The selector I45 comprises a moving contact arm I41 for contacting the condensers I 43, I44, and I45 (positions 1, 2 and 3 respectively) having different values of capacitance whereby each of these condensers cooperates with corresponding elements associated with control units 86, 89, etc., whereby the. track switches I6, I1, etc, may be selectively operated. Each of the condensers I43, I 44, and I45 have one of their terminals connected to the conductor I46, which is connected to the trolley wheel 44 contactin bus bar 46. The other terminals of condensers I43, I44, and I45 are adapted to be contacted by the moving contact arm I41, which is connected to current collecting trolley 5'! through conductors I48, I49, and I55. Since trolley wheel 44 and trolley wheels M and 42 (trolley 31) are running on the same bus bar 46, it is apparent that condensers I43, I44, and I45 normally have no voltage applied to them.

The control unit 88 comprises an inductance 1 I5I and a condenser I52 connected in a series circuit and adapted to be connected in series with one of the condensers I43, I44, and I45 (Fig. 5). The condenser I43 of the selector I40 has a value such that the series circuit of condenser I52,

inductance I5I, and condenser I 43 resonates to' the bus bar frequency, '60 cycles, for example. For resonance 2 /LC where f is the frequency of the circuit voltage in cycles per second, 11' is equal to 3.1416, L is the inductance of the circuit in henries and C is the capacity of the circuit in farads. Since the circuit frequency is a constant, for example, sixty cycles, and the inductance I5! is fixed in value it follows that the capacity C must always have the same value for resonance. Thus the combination of condensers I 43 and I52 in series must satisfy the above relationship. Two condensers C1 and C2 connected in series have a total capacity given by the law 1+C 1x 2 The capacity of condensers I43 and I52 being C143 and C152, the capacity for resonance at control unit 88 is If however either of the capacities I44 and I45 were substituted for capacity I 43, the total capacity would be different and there would be no resonance at control unit 88.

The control unit 88 also includes a glow discharge tube I54 whose discharge is controlled by a voltage derived from the inductance I5I when the circuit including the inductance I5I, condenser I52, and the condenser I43 is completed, and a relay I55 operated by current supplied through tube I54 to control the energization of coil 64 of contactor 58 to thereby effect operation of track switch I6. Whenever a series circuit is resonating, a high voltage appears across the elements of that circuit, for example, the inductance I5I of the circuit comprising inductance I5! and condensers I52 and I 43. However, when a series circuit is not resonating, the voltages across the elements thereof are low. Since condensers I44 and I45 have values of capacity differing from that for condenser I43, from the above law, there will be'no resonance when these condensers are connected in series circuit with condenser I52 and inductance I5I, and accordingly insufficient control voltage is obtained.

Electron tube I54 is of a cold cathode glow discharge type having a plate I56, a cathode I51, and a control electrode or grid I58. Accordingly, when a voltage is applied between the cathode 51 and the plate I56, and a voltage of proper value is applied to grid I 58, the tube will conduct current to operate relay I55. Since tube I54 is of the glow discharge type, once current begins to flow therein it continues to flow until the plate voltage is removed or reduced to a low Value, as is well understood. This occurs every negative half cycle of the bus "bar frequency.

The relay I55 supplied with current through tube I54 is of a Well :kno-wn'type including a pair of contacts I59 and a coil I6! for operating the contacts. and are held closed onlyso long as coil I61 carrying current. Whenever there isnocurrent in cell I6I, contacts I59 remain open. Coil I6I is connected in the plate circuit of tube I54 so that the total current conducted by tube I54 will flow therethrough. Plate voltage is constantly supplied to tube I54 through a circuit extending from L1 through resistor I52, conductor I63, coil I6I, plate I56ycathode I51, and conductor I-64 to L2. Connected to resistor I62 and conductor I53 is a resistor I65 which is connected at its other end to L2 and conductor I54. Resistors I62 and IE5 accordingly form a potentiometer whereby any desired proportion of the voltage existing across L1 and L2 may be applied between the cathode and plate of tube I54. Since the voltage existing across L1 and L2, and hence existing across the cathode and plate of tube I54, is an alternating voltage, it follows that tube I54 conducts onlyimpulses of current whenever grid I58 is sufficiently energized. In order to smooth out these current fluctuations in coil I6I, the

con-denser I55 is connected across the coil ter- The contacts I59 are normally open I 9|, a voltage is applied to these elements as will be explained subsequently. In order tosupply a control voltage to grid I58, the grid I58 is connected through a resistor I69 to the mid-point of a pair of resistors HI and I12, the other terminals of these resistors being connected respectively across inductance II to conductors I66 and I61. The resistors HI and I12 form a potentiometer whereby any desired proportion of the voltage appearing across inductance I5I may be applied to grid I58. Hence, when inductance I5I forms part of a resonating circuit, a high voltage appears thereacross, and is therefore applied to grid I58 to fire or initiate conduction through tube I54, but when inductance I5I is not part of a resonating circuit voltages appearing across it are too low to fire the tube I54. Accordingly, when conveyor I5 moves by control conductor 9| and the movable terminal I41 is connected to condenser I43 (position 1 of selector I40), the inductance I5I is part of a resonating circuit and the tube I54 fires and conducts current through coil I6I through the plate circuit described to actuate relay'I55, thereby controlling operation of track switch I6. But when movable terminal I41 is connected to condensers I44 or I45 (positions'2 or 3 of selector I40), the inductance I5I is not part of a resonating circuit and no control voltage is supplied to tube I54.

The conveyor propulsion motor 35 has power supplied to it through conductors I13 and I14 and conductors from current collectors 36 and 31 including the trolleys 38, 39, and M, 42 (Fig. 2). In order that the power flow to the motor 35 from the'trolleys 36 and 31 is not interrupted when the trolleys pass over the various control operate the toggle mechanism, the coils I81 and I88 are provided, coil I81 operating an armature to straighten the toggle mechanism I86 for closing contacts I85, and coil I88 operating an armature to trip the toggle mechanism for opening contacts I'85. The opening coil I88 may be energized through the stop push button I89 (push button switch 50 comprises push buttons I89, I9I, I92 and I93), or it may be energized by means of receiver I42 when the conveyor approaches the desired stopping station, as will be explained. To actuate the conveyor to move forwardly without the supervision of an operator, the contacts of the automatic push button I9I are closed to energize coil I81 and to control the conveyor to move forwardly or rearwardly in small amounts, i. e., inching, the contacts of the forward push button I92 or the contacts of the reverse push button I93 are closed which close circuits tocoils I19 and I83 respectively.

The receiver I42 for energizing coil I81 when it is desired to stop the conveyor automatically comprises a relay I94, an electrontube I95 for supplying current to relay I94, and a series circuit consisting of an inductance I96 and one of the condensers I91, I98, I99 and 20I, the series circuit forming means cooperating with the condensers at the various stop stations to provide a resonating circuit for controlling triggering or firing of electron tube I95. The condensers I91, I98, I99 and 20I along with the movable contact arm adapted to engage one terminal thereof comsections (which include control conductors and insulators separatingthem from the bus bars) the spacing of the trolley wheels M and 42, and 38 and 39, is such that the trolleys span over the control sections and thus one of the trolley wheels of each collector is in contact with the bus bars at all times. The motor is a three-phase I 16 are provided, the contactor I15 controlling the motor to run in the forward direction, and

the contactor I16 controlling the motor to operate in the reverse direction. The contactor I15 is of a well known type including the normally open pairs of contacts I11 and I18 adapted to be operated by a normally unenergized coil I19. Contacts I11 and I18 are held closed only so long as coil I 19 is energized. Similar to contactor I 15, contactor I16 includes normally open pairs of ;contacts I 8I and I82 adapted to be closed by a normally unenergized coil I83, the contacts I8I and I82 being closed only so long as coil I83 is energized.

In order that the conveyor be capable of moving in the forward direction without supervision,

the contacts I11 and I18 of contactor I15 may be held closed through the continuous energization of coil I19 by the latching relay I84 which includes a pair of contacts I85 adapted to be closed by an over-center toggle mechanism I86. To

prise a stop station selector 200 having positions 1, 2, 3 and 4 (Figs. 1 and 2) corresponding to the condensers respectively. Relay I94 is of a well known type having a pair of normally open contacts 202, and a coil 203 for operating the contacts, the contacts 202 remaining closed only so long as coil 203 is energized. The coil 203 is in the plate circuit of electron tube I95 whereby this tube controls operation of the relay.

Electron tube I95 similar to tube I54 is of the cold cathode glow discharge type having a plate 204, a cathode 205, and a control electrode or grid 206. Plate voltage is supplied to the tube through the circuit extending from L1, bus bar 46, trolley wheels M and 42, conductor I50, conductor I49, conductor 201, resistor 208, conductor 209, coil 203 of relay I94, conductor- 2I I, plate 204, cathode 205, conductor 2I2, conductor 2I3, conductor 2I4, and conductor 2I5 to trolley wheels 38 and 39 through the bus bar 41 (Fig. 2) to L2. Connected from resistor 208 and conductor 209 to the junctures of conductors 2I2 and 2I3, is the resistor 2I6. Resistors 208 and 2I6 in series are connected directly across the source of supply L1 and L2 as will be seen from the circuits described, and accordingly form a potentiometer so that any desired amount of the supply voltage may be applied to the cathode plate circuit of tube I95. Control grid 206 is connected through a conductor 2I1 and through a resistance 2"! to the junction of the two resistances 2I9 and 220, as shown. The resistance 2I9 is connected by means of a conductor 222 to one side of inductance I96, and resistor 220 is connected by means of a conductor 223 to the other side of inductance I96. Resistors 2 I 9 and 220 in series are connected across inductance I 96 and constitute a potentiometer whereby any desired portion of the voltage appearing across the inductance may be applied to control grid 206.

The responsive circuit for supplying a voltage to grid 206 consists of inductance I96, one of the condensers I91, I98, I99, and 20I, and condenser 13 at one of the stop stations (Fig. 4). When the proper combination of inductance and capacitance is made, the series circuit to which the frequency of the source is supplied resonates. As pointed out previously the law defining electrical resonance is where L is the value of inductance I96 and C is the value of capacity combinations which satisfy this law. When the circuit resonates a high voltage appears across the inductance I96 and accordingly the tube I95 fires and permits current to flow through coil 293 through the plate circuit described, thereby energizing coil I88 to stop the conveyor. Whenever the combination of total capacitance and inductance I96 is such that the series circuit formed is not in resonance, the voltage derived from inductance I95 is not sufiicient to fire the tube I95. The tube I95 conducts only short impulses of current since the voltage applied to its plate is alternating, and therefore the tube becomes non-conductive during a portion of every cycle. Since coil 203 therefore receives only short impulses of current, condenser 223 is connected across it to smooth out the voltage fluctuations.

Condensers I91, I98, I99, and 2III each have one of their terminals connected to conductor 224 which is in turn connected to trolley wheel 43, and hence is connected to L2 or the source of supply. The other terminals of the condensers are connected by means of a moving contact 225 through a conductor 226 to inductance I96 and therethrough to conductor 2| 4, and thence through conductor 2I5 to the trolley collectors 38 and 39 and the source of supply L2. Therefore when a conveyor is not at a stop station, the voltage applied to the circuit consisting of the inductance I96 and one of the associated condensers is zero since collectors 43, and 38 and 39 are running on the same bus bar. The values of capacitance of condensers I91, I98, I99 and 29I are each difierent from each other so that circuits completed with the condensers at the various stop stations will form responsive or resonant circuits only at the desired stop stations. Thus condenser I91 (position 1 of selector 299) cooperate with the condensers at stop stations 2| and 25, condenser I98 (position 2 f selector 299) cooperates with condensers at stop stations 22 and 25, condenser I99 (position 3 of selector 209) cooperates with condensers at stop stations 23 and 21, and condenser 29! (position 4 of selector 290) coopcrates with condensers at stop stations 24 and 28. The total capacity of two condensers in series follows the law previously given. Thus to have resonance at stop station 2I, condenser H1, and condenser I91, having capacity values C117 and C197, have a total capacity I C: C117 197 117 X 197 which satisfies the law cooperating: condensers as indicated have propervalues. I

With the foregoing description of structure in mind, the remainder of the structure and the operation of the system may best be set forth by considering the different aspects of the system as predeterminedly controlled conveyors move through it.

The first type of operation is that of a conveyor moving along trunk trackway portion II and having its final position predetermined so that it will stop at stop station 22 (Fig. 2). This requires that the track switch I6 be moved to its curved track position, i. e., trackway 54 registers with branch trackway I3, and further that the conveyor move past stop station 2i Without stopping. The track switch selector I49 is set to position I, contact arm I41 contacts the terminal of condenser I43, and the stop station selector 290 is set to position 2, contact arm 225 contacts the terminal of condenser I98.

To start the conveyor moving, the operator pushes the automatic button I9I (Fig. 2) closing the circuit extending from L1, bus bar 46, trolley .wheels 4| and 42, conductor I50, conductor I49, closed contacts of automatic switch I9I, conductor 22I, coil I81, conductor 239, conductor 221, conductor 228, conductor 229, conductor 2I5, trolley wheels 38 and 39, and bus bar 41 to L2. This circuit energizes coil I81 to straighten out the overcenter toggle I96 to close contacts I85. Closing contacts I energizes the coil I19 throu h a circuit extendin from bus bar 46, trolley Wheels 4| and 42, conductors I59 and I49, conductor 23I closed contacts I85, conductor 232, coil I19, conductors 228, 229, and 2I5, and trolley wheels 38 and 39 to bus bar 41. Energizing coil I19 picks up the relay I15 and closes contacts I11 and I18, and since relay I94 is mechanically latched, contacts I11 and I18 remain closed. Closing contacts I11 and I18 supplies power to motor 35 through a circuit extending from bus bar 46 through trolley wheels II and 42, conductor I59, conductor 233, closed contacts I18, conductor I13 to motor 35, and from bus bar 41 through current collectors 38 and 39, conductor 215, conductor 234, closed contacts I11, and conductor I14 to the motor. The motor is thereby energized by connecting conductors I13 and I 59, and conductors I14 and 2 I 5 to run in the forward direction.

As the conveyor moves forward onto the'trunk trackway portion I 2, the trolley wheel 42 contacts the control conductor 9| completing a circuit from bus bar 46'through trolley wheels II and 42, control conductor 9I, conductor I69, condenser I52, inductance I5I, and conductor I66 to L2. The 69 cycle voltage of the system is therefore applied across the condenser I52 and inductance I5I in a series circuit. However, the combination of inductance I5I and condenser I52 does not resonate to the frequency of the system, and accordingly no control impulse is applied to tube I54. When trolley wheel 4I contacts control conductor 9|, condenser I52 and inductance I5I also receive a voltage impulse as described for trolley wheel 42, but this also produces no voltage im pulse applied to tube I54. As the conveyor continues to move along trunk trackway portion I2, the trolley 44 contacts control conductor 91 (the trolley 44 bein spaced from trolley 4| a distance sufficient so that trolley 4| is past control conductor 9| before trolley 44 contacts it). This situation is illustrated in a more simplified form in Fig. 5. Referring to Fig. 5 as well as to Fig. 2,

15 acircuit is completed extending from L1 or bus. bar 46 through current collecting trolleys M and 42, conductors I58, I49,.and I48, contact arm I41, condenser I43, conductor I46, trolley 44, control conductor 9|, conductor I68, condenser I52, ,inductance I I, and conductor-I66 to L2. It is seen that the condenser I43, the condenser I52, and the inductance I5I are in a series circuit. Moreover, the value of the total capacitance of condensers I43'and I52 is such that with inductance I5I a circuit resonatin to the power supply frequency is formed. Accordingly, a high voltage appears across the inductance I5! and tube I54 fires to pass current since there is a plate voltage applied to it; as previously described. Current conducted by tube I54 passing through coil Iti of relay I55 picks up this relay and closes the contacts I58. If the contact arm '44 had been connected to either ofthe condensers I44 and I45, the series circuit includin either of these condensers, the condenser I52, and the inductance I5I would not have been a circuit resonating to the frequency of the power supply, and hence the tube I54 would not have become conducting. As a conveyor moves along, trolley 44 remains on control conductor 9I only a very short interval, and hence tube I54 remains conducting only for a very short interval. Consequently the relay coil I6I maintains its contacts I59 closed only for a short interval. This short interval, however, produces a control impulse to effect movement of the track switch.

I Closing contacts I59 energizes coil 64 of contactor 58 through the following circuit: From L1 through conductor 235, closed contacts I59, conductor 236, conductor 231, closed contacts of limit switch "II, conductor 238, coil 64, conductor 239, and conductor 24 I .to L2. Energizing coil 64 closes pairs of contacts 6I, 62, and 63, the closed contacts 6I forming a holding circuit for coil 64 as follows: From L1 through conductor 242, closed contacts 6I, conductor 243, conductor 231, closed contacts of limit switch II, conductor 238, coil 64, conductors 239 and 24I to L2. Therefore, when relay contacts I59 are opened, the coil '14 remains energized. Closing contacts 62 and 63 supplies power to motor 55 for moving track switch I6 to the curved trackway position through circuits extending from L1 through conductor 244, closed contacts 62, conductor 245, and conductor 246 to motor 55, and from L2 through conductor 24?, through closed contacts 63, through conductor 248 and conductor 249 to the motor 55. L1 and L2 thus are connected respectively to conductors 243 and 249 to run motor 55 in the desired direction, the third terminal of motor 55 being a ground connection (L3). The motor 55 continues to run until the track switch I6 reaches the posi tion where trackway 54 registers with branch trackway I3 and trunk trackway portion I2 at which position the contacts of limit switch H are opened, thereby de-energizin the coil 64 to effect opening of contacts 62 and 63. Conse quently, the power supply to themotor 55 is interrupted and the track switch I6 becomes stationary.

The conveyor now moves through on curved trackway 54 and onto the branch trackway I3. As soon as the trolley wheel 42 contacts the control conductor 91 (the complete conveyor has moved through the track switch and is on branch trackway I3), the following circuit is completed to energize coil 68 of contactor 59 to shift track switch I6 back to the straight trackway position:

* From-L1, bus bar 48, trolleys 4I and 42, control impulses of the bus bar voltage. This is harmless conductor 91, conductor 25I, conductor 252 through coil 66, conductors 239 and 24I to L2;

Energizing'coil 68 closes pairs of contacts 65, 66, and 67, contacts 61 forming a holding circuit for coil 68 as follows: From L1 through conductor 253, conductor 254, closed contacts 61, conductor 255, closed contacts of limit switch 69 (these contacts are closed when track switch I6 moves away from the straight trackway position), conductor 256, conductor 252 through coil 59, conductors 239 and 24I to L2. Therefore, when trolley c01- lectors 41 and 42 leavecontrol conductor 91, relay coil 68 remains energized. Closing contacts 66 and 61 supplies power to motor to run in the reverse direction through circuits extending from L1 through conductor 253, conductor 251, closed contacts 65, conductor 258 and conductor 249 to motor 55, and from L2 through conductor 24I,

conductor 259, closed contacts 66, conductor 26I,

and conductor 246 to motor 55. L1 and L2 have now been connected to conductors 249 and 246 respectively, thereby reversing the connection to motor 55 which runs in the reverse direction to I move track switch I6 to the point where trackway 53 registers with trunk trackway portion I2. At this point the contacts of limit switch 69 are opened by the track switch I6 to interrupt the circuit to coil 68, thereby opening contacts 65 and 66. Consequently, the motor 55 stops.

The conveyor continues to move in the direction of the arrow along branch trackway I3, moving past stop station 2I without stopping, and approaching stop station 22. At stop station 2|, however, the current collectin trolleys 38 and 39 span from bus bar 49 to control conductor H8, thereby completing a circuit from L2, bus bar 49, through current collecting trolleys 38 and. 39, control conductor II8, conductor 262, condenser II'I, and. conductor 263 to bus bar 48 (L1). Accordingly,the condenser I I7 is subjected to two and may be neglected since no control circuits are completed and the condenser II'I may easily be constructed to withstand the voltage. As the conveyor approaches stop station 22, the trolley lecting trolleys 38 and 39, control conductor I23,

conductor 264, condenser I22, and conductor 265 to bus bar 48. Here also the condenser I22 is subjected to the voltage of the system.

As the conveyor continues to move along trackway I3, the trolley wheel 43 contacts control conductor I23 as is shown best in Fig. 4. Referring to Figs. 4 and 2, when trolley 43 contacts control conductor I23 at stop station 22, a circuit is completed extendin from L2, bus bar 49, trolley wheels 38 and 39 through conductors 2I5 and 2M, inductance I96, conductor 226, contact arm 225, condenser I98, conductor 224, trolley wheel 43, control conductor I23, conductor 264, condenser I22, and conductor 265 to bus bar 48 or L1. It is seen that the condenser I22, the condenser I93, and inductance I96 are in a series circuit across the source of supply L1 and L2.

Since condenser I98 was selected with-a capacity through coil 203 of relay I94 which picks up and closes contacts 202.

Closing contacts 202 completes a circuit to coil I88 for tripping the over-center mechanism I86 as follows: From bus bar 48 (Figs. 2 and 4), trolley wheels M and 42, conductor I50, conductor I49, conductor 266, closed contacts 202, conductor 261, conductor 268 through coil I88, conductor 269, conductors 221, 228, 239, and 2I5 to trolley wheels 38 and 39, and bus bar 49. Energizing coil I88 trips the over-center mechanism I86, opening contacts I85, and accordingly de-energizing the coil I19 which opens contacts I11 and I18 to stop motor 35, and hence the conveyor, at sto station 22. The conveyor of its own momentum will move past control conductor I23 whereby the circuit through condensers I22 and I98 and inductance I96 is de-energized.

Referring to Fig. 4, and noting the series resonant circuit formed by condensers I22 and I98 and inductance I96, it will be readily understood that since condenser I I1 (stop station 2 I) differs from condenser I22, that when conveyor I moved past stop station 2I the condenser II1 did not cooperate with condenser I22 to form a resonant circuit with inductance I96. Similarly, when the conveyor continues to move along branch trackway I3 and contact arm 225 is allowed to remain connected to condenser I 98, the conveyor will not stop at stations 23 and 24 since the condenser I98 will not cooperate with the condensers at these stop stations to form a resonant circuit.

To start the conveyor moving again, the operator pushes the automatic button I9I thereby energizing coil I81 through a circuit previously described, but having its origin in this position on bus bars 48 and 49 instead of 46 and 41. Accordingly the motor 35 is energized to continue the conveyor in this movement so that it approaches the track switch I8. Assume that the track switch I8 is in the position shown solid in Fig. 3. Itwill' be necessary that the track switch be moved so that curved trackway 13 registers with branch trackway I3, and trunk trackway portion I0. Accordingly, when trolley wheel 42 contacts the control conductor I04, a circuit is completed to energize coil 82 of contactor 11, as follows: From L1, bus bar 48 through trolley wheels M and 42, control conductor I04, conductor 21I, conductor 212, coil 82, conductor 213, conductor 214, and conductor 215 to L2. Energizing coil 82 picks up relay 11 to close contacts 19, 80, and Ill, the contact 19 forming a holding circuit for coil 82 as follows: From L1 through closed contacts of limit switch 86, conductor 216, closed contacts 19, conductor 211, conductor 212, coil 82, and conductors 213, 214, and 215 to L2. Thus, when the trolley wheel 42 moves ofi of control conductor I04, relay coil 82 remains energized.

Closing contacts 80 and 8| supplies power to motor 14 as follows: From L1 through conductor 218, conductor 219, closed contacts 80, conductor 28I, and conductor 282 to motor 14, and from L2 through conductors 215 and 214,.conductor 283, closed contacts 8|, conductor 284, and conductor 285 to motor 14. The motor 14 is a threephase motor, one terminal of which is grounded as shown. Power is thus supplied to the motor to move track switch I8 to the curved trackway position, and when this position is reached the contacts of limit switch 88 are opened to deenergize coil 82, thereby opening contacts 80 and 8I to deenergize motor 14 and to stop track switch I8. The conveyor then moves through the track switch I8 onto trunk trackway portions I0 and I I in the direction of the arrows. The first phase of the operation is now completed.

The second phase of operation occurs when a conveyor is predeterminately controlled to move onto branch trackway I4 and to stop at any of the stop stations therealong, for example, stop station 21. To effectuate this condition, assuming that the conveyor begins its movement on trunk trackway portion II, contact arm I41 is connected to condenser I44 (position 2 of track switch selector I40, Fig. l) and contact arm 225 is set to be connected to condenser I919 (position.

3 of stop selector 200, Fig. 1). To start the conveyor moving the operator closes automatic push button I9I as previously described. When. the conveyor approaches control conductor 9I associated with track switch I6, the control unit 88,v

is not energized since the condenser' I44 when connected in series circuit with condenser I52 and inductance I5I (Fig. 5), the circuit does not resonate to the power supply frequency and hence no control impulse is applied to tube I54. Accordingly, the conveyor moves past track switch I6 and approaches track switch I1. Since control unit 89 is identical with control unit 88, with the exception of the fact that the condenser I52 for control unit 88 is different than the corresponding condenser for control unit 89, the value of this latter condenser being such that when combined with condenser I44, and the inductance at control unit 89, control unit 89 is energized tomove track switch I1 to the curved trackway position to allow the conveyor to move through onto branch trackway I4. Similarly to branch trackway I3, when the trolley wheels M and 42 contact the control conductor IOI in branch trackway I4, circuits are energized to move track switch I1 back to the straight or through trackway position. It is believed that the operation of track switch I1 as thus briefly described will be clear by reference to the circuits and apparatus described in connection with track switch I6. 7

As the conveyor moves along on branch trackway I4, the condensers at the stop stations 25 and 26 are of course contacted .by the trolley wheel 43 to complete circuits withcondenser I98 and inductance I96 carried by the conveyor. However, these condensers do not have. the proper values of capacitance to cooperate with condenser I99 and inductance I96 to provide a circuit resonating to the power supply frequency. When the conveyor reaches stop station 21 and the trolley wheel 43 contacts the control conductor I 31, a circuit similar to that shown in Fig. 4, but comprising the condenser at stop station 21, condenser I99, and inductance I86 is completed. This circuit resonates to the power supply frequency and hence a voltage impulse is applied to control grid 286 of tube I to effect stopping of the conveyor propulsion motor 35, as already described. By closing the automatic push button I9I, the conveyor may again be started,

and it will move past stop station 28 without stopping since the condenser at this station does not combine'with condenser I99 to effect a resonating circuit. I

When the conveyor approaches track switch I9, as described for the first aspect of conveyor operation, the track switch I9 is controlled to move to the curved trackway position when trolley wheel 42 contacts control conductor III. The conveyor then moves through track switch I9 onto trunk trackway portion I8, and moves track switch must be moved to the through trackway position. When trolley wheel 42 contacts the control conductor I01, a circuit is completed to energize coil 900i contactor 18 through a circuit as follows (Fig. 3) From L1, bus bar 46, trolley wheels M and 42, control conductor I01, conductor 285, coil 90, conductors 213, 214 and 215 to L2. Energizing coil'90 picks up contactor 18 to close contacts 83, 84 and 85, the contacts 85 forming a holding circuit for coil 90, as follows: From L1 through closed contacts of limit switch 81 (thesecontacts are closed when track switch I8 moves away from the straight trackway position), through conductor 281, closed contacts 85, conductor 288, conductor 289, coil 90, through conductors 213, 214, and 215 to L2. Therefore, coil 85 remains energized when trolley wheels M and 4-2 move away from control, I01.

Closing contacts 83 and 84 supplies power to motor 14 through circuits as follows to run in the reverse direction to move track switch I8 to the straight or through trackway position: From L1 through conductor 218, closed contacts 84, conductor 29I, conductor 285 to motor 14, and from L2 through conductor 215, conductor 292, closed contacts 83, conductor 293, and conductor 282 to motor 14. L1 and L2 are thus connected to conductors 285 and 282 to operate motor 14 in the reverse direction. When the track switch reaches the straight trackway position, contacts of limit switch 81 are opened to de-energize coil 90, efiecting opening of contacts 83, 84 and 85 to de-energize the motor 14 and thereby stopping the track switch. The conveyor continues its movement through track switch I8 and onto the trunk trackway portion II. The second phase of operation is now completed.

In the third phase of operation, it is predetermined that the conveyor will move past both track switch I6 and I1 to a track switch at some other point in the conveyor system, and. is also predetermined to stop at some other point on a branch trackway associated with that track switch. Accordingly, the moving contact 141 is connected to condenser I45 (position 3 of the track switch selector I40, Fig. 1) and the moving contact 225 is connected to condenser 20I (position 4 of the stop selector 280, Fig. 1). Thus when the conveyor approaches track switches I6 and I1, there are no resonating circuits completed with the inductances and condensers arranged at control units 88 and 89, and the conveyor moves on to some other track switch which will'be operated. As the conveyor moves on to the third branch trackway, it will move along the various stop stations until the condenser arranged at a particular stop station cooperates with condenser 20I and inductance I98 to form a resonant circuit, thereby effecting stopping of the conveyor. Continuing to move along this branch trackway, the conveyor moves onto trunk trackway portion I0, and eventually the trolley wheel 42 contacts control conductor II4 to cause track switch I9 to move to the through trackway position and permit theconveyor to move through, and similarlymove through the track switch I8 by virtue of trolley wheel 42 contacting control conductor I01. The conveyor then moves on to trunk trackway portion II. The

third phase of operation is complete.

The three examples of operation illustrate the modes of operation of conveyors in the system. While the operation has been described in connection with only one conveyor I5, it will be understood without additional illustration that numerous conveyors similar to conveyor I5 may move on the various trackways, each of such conveyors having selectors corresponding to selectors I48 and 208 whereby the conveyor movements are predeterminedly controllable. In each case the apparatus carried by the conveyors is connected into electrical circuits when the trolleys contact the control conductors 9| or 34 for track switch operation and contact the control conductors 2I24 or 25-28 for controlling conveyor stopping, the control conductors forming part of the bus bar system. The control conductors SI and 94 are connected through circuits including inductances and capacities of different values to one side of a source of power supply. Since the inductances and capacities form difierent values of impedance, the control conductors 8i and 84 are electrically diiferentiated from each other and consequently are discriminating in their cooperation with apparatus carried by the conveyor. Thus the control conductors discriminate between different conveyors as to which one will set off movement of a track switch. Similarly at each of the stop stations in branch trackway I3, for example, the condensers are connected to control conductors H8, I23, I26 and I28 respectively, the condensers also being connected to one side of the source of supply. The capacitance values of the condensers being different, they form different impedance values and thus these control conductors are also electrically differentiatedfrom each other and hence are discriminating in their cooperationv with conveyor carried apparatus. Accordingly the control conductors discriminate between different conveyors as'to which one will stop at which stop station. Each control conductor constitutes in effect an electrically different source of supply waiting for the proper cooperating apparatus to be connected to it. Correspondingly the trolleys 43 and 44 of the different conveyors have different values capacitance, and capacitance and inductance connected to them respectively. These elements having different values of impedance, the trolleys are also electrically differentiated from each other.

While a particular embodiment of the invention has been shown it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated by the appended claims to cover any such modifications as come within the true spirit and scope of the invention. Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

l. Conveyor apparatus comprising a trackway including a trunk trackway and a plurality of branch trackways, a plurality of motor operated track switches for connecting said branch trackways to said trunk trackway, bus bar means disposed along said trackways including energized sections interrupted by a gap adjacent each track switch, bus bar portions differentiated electrically reactively from each other connected to a source of power and disposed in the gaps between said energized sections, meansassociated with each track switch for controlling movement thereof into connection with said trunk trackway, one

each of said track switch movement controlling means being associated with the one of said differentiated bus bar portions adjacent said each track switch, conveyors adapted to move on said trackways, and individual current collecting means also differentiated electrically reactively from each other carried by each of said conveyors for cooperation with said differentiated bus bar portions when connected thereto for selectively determining which of said track switch movement control means is energized, said current collecting means being adapted to contact said energized bus bar sections whereby said differentiated bus bar portions and said differentiated collector means are sequentially connected to eachother during conveyor movement.

2. Conveyor apparatus comprising a trackway, including a trunk trackway and a plurality of branch trackways, a plurality of motor operated track switches for connecting said branch trackways to said trunk trackways, bus bar means disposed along said trackway including energized sections interrupted by a gap adjacent each track switch, bus bar portions differentiated electrically reactively from each other connected to a source of power and disposed in the gaps between said energized sections, means including an electron tube trigger circuit associated with each track switch and associated with the bus bar portion adjacent said each track switch for controlling movement thereof to connect the associated branch trackway to said trunk trackway, conveyors adapted to move on said trackways, and individual current collecting means also differentiated electrically reactively from each other carried by each of said conveyors for cooperation with said differentiated bus bar portions when connected thereto for selectively determining which of said trigger circuits has its operation initiated, said current collecting means being adapted to contact said energized bus bar sections whereby said differentiated bus bar portions and said differentiated collector means are sequentially connected to each other during conveyor movement.

3. Conveyor apparatus comprising a trackway, a plurality of stop stations arranged therealong, bus bar means disposed along said trackway including energized sections interrupted by gaps adjacent said stop stations, bus bar portions differentiated electrically reactively from each other connected to a source of power and disposed in the gaps between said energized sections, conveyors adapted to move on said trackway, stop control means carried by each of said conveyors, and individual current collecting means also differentiated electrically reactively from each other carried by each of said conveyors for cooperation with said differentiated bus bar portions when connected thereto for selectively determining which of said stop control means is energized, said current collecting means being adapted to contact said energized sections whereby said differentiated bus bar portions and said differentiated collector means are sequentially connected to each other during conveyor movement.

4. Conveyor apparatus comprising a trackway including a trunk trackway and a plurality of branch trackways, a plurality of track switches for connecting said branch trackways to said trunk trackway, bus bar means disposed along said trackway including energized sections interrupted by gaps adjacent each track switch, bus bar portions insulated from said energized sections. disposed in said gaps, a plurality of-inductive reactive circuits connected to asource of alternating voltage having a predetermined frequency, one of said plurality of inductive, reactive circuits being associated with each track switch and being connected to the bus bar portion disposed in the gap adjacentsaid each track switch, a plurality of conveyors adapted to move along said trackways, contact means carried by each of said conveyors, capacitive reactivemeans carried by each of said conveyors connected to the contact means associated therewith and connected to said source of alternating voltage, each of said inductive reactive circuits when connected to certain ones of said capacitive reactive means forming a circuit resonant to a voltage having the frequency of said source, said contact means being adapted to contact said energized sections and said bus bar portions and during conveyor movement sequentially connecting said inductive reactive circuits and said capacitive reactive means in individual electric circuits, therebyto form resonating circuits only when individual ones of said inductive reactive circuitsare connected to said certain ones of said capacitive reactive means, and control means associated with each track switch and adapted to have energization thereof effected by the associated inductive reactive circuit when forming part of a resonating circuit for efiecting connection of the track switch with said trunk trackway.

5. Conveyor apparatus comprising a trackway, bus bar means disposed along said trackway including energized sections interrupted by a plurality of spaced gaps, bus bar portions insulated from said energized sections disposed in said gaps, a plurality of inductive reactive circuits, one each of which is connected to each of said bus bar portions and to a source of alternating voltage having a predetermined frequency, a plurality of conveyors adapted to move along said trackway, contact means carried by each of said conveyors, capacitive reactive means carried by each of said conveyors connected to said source of alternating voltage and to the contact means asso ciated with said each-conveyor, each of said inductive reactive circuits when connected to certain ones of said capacitive reactive means forming circuits resonant to a voltage having the frequency of said source, said contact means being adapted to contactsaid energized sections and said bus bar portions and during conveyor movement sequentially connecting said inductive reactive circuits and said capacitive reactive means in individual electric circuits, thereby to form a resonating circuit only when individual ones of said inductive reactive circuits are connected to said certain ones of said capacitive reactive means, and conveyor control means associated with each of said inductive reactive circuits, individual ones of said control means being adapted to have energiz ation thereof effected by the associated inductive reactive circuit when forming part of a resonating circuit.

,6. Conveyor apparatus comprising a trackway, a plurality of stop stations spaced along said trackway, bus bar means disposed along said trackway including energized sections interrupted by gaps one each of which is adjacent each stop station, bus bar portions insulated from said energized sections and disposed in said gaps, a plurality of capacitive reactive means one each of which is connected to each of said bus bar portions and connected to a source of alternating voltage having a predetermined frequency, a

plurality of conveyors adapted-to move along said trackway, contact means carried by each of said conveyors, inductive reactive circuits carried by each of said conveyors connected to said source of alternating voltage and to the contact means associated with said each conveyor, each one of said inductive reactive circuits when connected to certain ones of said capacitive reactive means forming a circuit resonant to a voltage having the frequency of said source, said contact means being adapted to contact said energized sections and said bus bar portions and during conveyor movement sequentially connections said inductive reactive circuits and said capacitive means in individual electric circuits, thereby to form a resonating circuit only when an individual one of said inductivev reactive circuits is connected to a certain one of said capacitive reactive means, and stop control means carried by each of'said conveyors and adapted to have energization thereof efiected by the inductive reactive circuit carried by said each conveyor only when forming part of a resonating circuit.

7. Conveyor apparatus comprising a trackway, a plurality of stop stations disposed along said trackway, bus bar means disposed along said trackway including energized sections interrupted by gaps adjacent each of said stop stations, bus bar portions insulated from said energized sections and disposed in said gaps, a plurality of ca-' pacitive reactive means connected to a source of alternating voltage, one each of said plurality of capacitive reactive means being associated with each of said stop stations and being connected to the bus bar portion disposed in the gap adjacent said stop station, a conveyor adapted to move along said trackway, contact means carried thereby, selectable inductive reactive circuits carried by said conveyor connected to said source of alternating voltage and to the contact means carried thereby, selected ones of said selectable inductive reactive circuits when connected to certain ones of said capacitive reactive means forming circuits resonant to a voltage having the frequency of said source, said contact means being adapted to contact said energized sections and said bus bar portions and during conveyor movemerit sequentially connecting a selected one of said inductive reactive circuits and said capacitive reactive means in individual electric circuits, thereby to form a resonating circuit only when said selected one of said inductive reactive circuits is connected to said certain one of said capacitive reactive means, and stop control means carried by said conveyor and adapted to have energization thereof effected by the selected inductive reactive circuit when forming part of a resonating circuit.

8. A trackway, a conveyor for travelling along said trackway, a power bus bar extending along said trackway, having a plurality of interruptions therein located at spaced distinguishable selectee stations alongside said trackway, a plurality of selectee bus bar means, one of said means being interposed at an interruption of said power bus bar at each of said stations, said bus bar means being in alignment with respect to said power bus bar and insulated therefrom, control collector means carried by said conveyor and guided to engage said power bus bar substantially continuously and to engage said interposed bus bar means sequentially as the collector means travel, a plurality .of distinguishable trackside circuit means having circuit elements of differing reactive characteristics located adjacent said stations and electricallyconnected to respective ones of said bus bar means, conveyor borne circuit means electrically connected to said collector means, said conveyor borne circuit means being connected to said trackside circuit means sequentially to complete electric control circuits energized by a common control power source of fixed predetermined frequency, said conveyor borne circuit means being manually adjustable as to its reactive characteristics to complete an electric control circuit resonant to said predetermined frequency only with the circuit means of a selected station, upon engagement of the collector means 1 with the bus bar means of the selected station,

and means included in said control circuit operably responsive only to a resonant condition within said circuit to control an operation affecting the conveyor at the selected station.-

9. A conveyor for travelling along a trackway, a power bus bar extending along said trackvvay, having a plurality of interruptions therein located at spaced distinguishable selectee stations alongside said trackway, a plurality of selectee bus bar means, one of said means being interposed at an interruption-of said power bus bar at each '0 fsai dstations and insulated therefrom, said bus bar means being in alignment with respect to said power bus bar, control collector means carried-by said conveyor and guided to engage said power bus bar substantially continuously and to engage said interposed bus bar means sequentially as the collector means travel, plurality of distinguishable trackside circuit means having circuit elements of difiering reactive characteristics located adjacent said stations and electrically connected to respective ones of said bus bar means, conveyor borne circuit means electrically connected to said collector means, said conveyor borne circuit means being connected to said tracks-i'de circuit mcanssequentially to complete electric control circuits energized by a common control power source of fixed predetermined frequency, said conveyor borne circuit means being-manually adjustable as to its reactive characteristics to complete an electric control circuit resonant to said predetermined frequency only with the circuit means of a selected station, upon engagement of the collector means with the bus bar means of the selected station, and means included in said control circuit operably responsive only to a, resonant condition within said circuit to control an operation affecting the conveyor at the selected station.

10. A trackway, a conveyor for travelling along said trackway, a power busbar extending along said trackway, having a plurality of interruptions thereinlocated at spaced distinguishable selectee stations alongside said tracl way, a plurality of selectee bus bar means, one of said means being interposed at an interruption of said power bus bar at each of said stations, said bus bar means being in alignment with respect to said power bus bar and insulated therefrom, control collector means carried by said conveyor and 25' gized by a common control power source of fixed predetermined frequency, said conveyor borne circuit means being manually adjustable as to its reactive characteristics to complete'an electric control circuit resonant to said predetermined frequency only with the circuit means of a selectedstation, upon engagement of the collector means with the bus bar means of the selected station, and means included in said control circuit operably responsive only to a resonant condition within said circuit to control an operation aifecting the conveyor at the selected station, said common control power source being connected to said power bus bar and through said collector means to said conveyor borne circuit means.

11. A trackway, a conveyor for travelling along said trackway, a power bus bar extending along said trackway, having a plurality of interruptions' therein located at spaced distinguishable selectee stations alongside said trackway, a plurality of selectee bus bar means, one of said means being interposed at an interruption of said power bus bar at each of said stations, said bus bar means being in alignment with respect to said power bus bar and insulated therefrom, control collector means carried by said conveyor and guided to engage said power bus bar substantially continuously and to engage said interposed bus bar means sequentially as the collector means travel, a plurality of distinguishable trackside circuit means having circuit elements of differing reactive characteristics located adjacent said stations and electrically connected to respective ones of said bus bar means, conveyor borne circuit means electrically connected to said collector means, said conveyor borne circuit means being connected to said trackside circuit means sequentially to complete electric control circuits, a common control power source of fixed predetermined frequency for energizing said control circuits, said conveyor borne circuit means being manually adjustable as to its reactive characteristics to complete an electric control circuit resonant to said predetermined frequency only with the circuit means of a selected station, upon engagement of the collector means with the bus bar means of the selected stations, and means included in said control circuit operably responsive only to a resonant condition within said circuit to control an operation affecting the conveyor at the selected station, said common control power source being connected to said power bus bar and through said collector means to said conveyor borne circuit means.

12. A trackway, a conveyor for travelling along said trackway, a power bus bar extending along said trackway, having a plurality of interruptions therein located at spaced distinguishable selectee stations alongside said trackway, a plurality of selectee bus bar means, one of said means being interposed at an interruption of said power bus bar at each of said stations, said bus bar means being in alignment with respect to said power bus bar and insulated therefrom, control collector means carried by said conveyor and guided to engage said power bus bar substantially continuously and to engage said interposed bus bar means sequentially as the collector means travel, a plurality of distinguishable trackside circuit means having circuit elements of diifering reactive characteristics located adjacent said stations and electrically connected to respective ones of said bus bar means, conveyor borne cir-' cuit means electrically connected to said collector means, said conveyor borne circuitmeans being connected to said trackside circuit means sequenlector means with the bus bar means of the selected station, and a translating device located on said conveyor and included in said control circuit and operably responsive only to a resonant condition within said circuit to control an operation afiecting the conveyor at the selected station.

13. A trackway, a conveyor for travelling along said trackway, a power bus bar extending along said trackway, having a plurality of interruptions therein located at spaced distinguishable selectee stations alongside said trackway, a plurality of selectee bus bar means, one of said means being interposed at an interruption of said power bus bar at each of said stations, said bus bar means being in alignment with respect to said power bus bar and insulated therefrom, control collector means carried by said conveyor and guided to engage said power bus bar substantially continuously and to'engage said interposed bus bar means sequentially as the collector means travel, a plurality of distinguishable trackside circuit means having circuit elements of diifering reactive characteristics located adjacent said stations and electrically connected to respective ones of said bus bar means, conveyor borne circuit means electrically connected to said collector means, said conveyor borne circuit means being connected to said trackside circuit means sequentially to complete electric control circuits energized by a common control power source of fixed predetermined frequency, said conveyor borne ation aifecting the conveyor at the selected station.

14. A trackway, a conveyor for travelling along said trackway, a propulsion motor carried by said conveyor, apower bus bar extending along said trackway, having a plurality of interruptions therein located at spaced distinguishable selectee stations alongside said trackway, a plurality of selectee bus bar means, one of said means being interposed at an interruption of said power bus bar at each of said stations, said bus bar means'being in alignment with respect to said power bus bar and insulated therefrom, control collector means carried by said conveyor and guided to engage said power bus bar sub stantially continuously and to engage said interposed bus bar means sequentially as the collector means travel, a plurality of distinguishable trackside circuit means having circuit elements of differing reactive characteristics located adjacent said stations and electrically connected to respective ones of said bus bar means, conveyor borne circuit means electrically connected to said collector means, said conveyor borne circuit means being connected to said trackside circuit means sequentially to complete electric control circuits energized by a common control power source of fixed predetermined frequency, said conveyor borne circuit means being manually adjustable as to its reactive characteristics to complete an electric control circuit resonant to said predetermined frequency only with the circuit means of a selected station, upon engagement of the collector means with the bus bar means of the selected station, and means included in said control circuit operably responsive only to a resonant condition within said circuit to interrupt the flow of electric power to said propulsion motor at the selected station.

15. A trackway, a conveyor for travelling along said traokway, a plurality of track switches in said trackway, a power bus bar extending along said trackway, having a plurality of interruptions therein located at spaced distinguishable selectee stations alongside said trackway, a plurality of selectee bus bar means, one of said means being interposed at an interruption of said power bus bar at each of said stations, said bus bar means being in alignment with respect to said power bus bar and insulated therefrom, control collector means carried by said conveyor and guided to engage said power bus bar substantially continuously and to engage said interposed bus bar means sequentially as the collector means travel, a plurality of distinguishable trackside circuit means having circuit elements of differing reactive characteristics located adjacent said stations and electrically connected to respective ones of said bus bar means, conveyor borne circuit means electrically connected to said collector means, said conveyor borne circuit means being connected to said trackside circuit means sequentially to complete electric control circuits energized by a common control power source of fixed predetermined frequency, said conveyor borne circuit means being manually adjustable as to its reactive characteristics to complete an electric control circuit resonant to said predetermined frequency only with the circuit means of a selected station, upon engagement of the collector means with the bus bar means of the selected station, and electric control means individual to said stations and sequentially included in said control circuit and operably responsive only to a resonant condition within said circuit to operate the corresponding track switch at the selected station.

16. A trackway, a conveyor for travelling along said trackway, a power bus bar extending along said trackway, having a plurality of interruptions therein located at spaced distinguishable selectee stations alongside said trackway, a plurality of selectee bus bar means, one of said means being interposed at an interruption of said power bus bar at each of said stations, said bus bar means being in alignment with respect to said power bus bar and insulated therefrom, control collector means carried by said conveyor and guided to engage said power bus bar substantially continuously and to engage said inter posed bus bar means sequentially as the collector means travel, a plurality of distinguishable trackside circuit means having circuit elements of differing reactive characteristics located adjacent a plurality of said stations and electrically connected to respective ones of said bus bar means, a plurality of trackside partial control circuits having circuit elements of differing reactive characteristics located adjacent others of said stations and electrically connected'to respective ones of said bus bar means, conveyor borne circuit means electrically connected to said collector means, said conveyor borne circuit means being manually adjustable as to its reactive characteristics to complete an electric control circuit resonant to a predetermined frequency of applied voltage only with the circuit means of a selected station, upon engagement of the collector means with the bus'bar means of the selected station, a translating device carried by said conveyor and included in said .control circuit and operably responsive only to a resonant condition Within said circuit to control an operation affecting the conveyor at the selected station, a conveyor borne partial control circuit electrically connected to said collector means and manually adjustable as to its reactive characteristics to complete an electric control circuit resonant to a predetermined fre quency of applied voltage only with the partial control circuit of a selected station, uponengagement of the collector means with the bus bar means of the selected station, and a plurality of translating devices located one each at the respective stations having said partial control circuits and sequentially included in said last-mentioned control circuit and operably responsive only to a resonant condition within said control circuit to control an operation affecting said conveyor at the selected station.

17. A trackway, a conveyor for travelling along said trackway, a plurality of track switches in said trackway, a propulsion motor carried by said conveyor, a power bus bar extending along said trackway, having a plurality of interruptions therein located at spaced distinguishable selectee stations alongside said trackway including track switch stations and stop stations, a plurality of selectee bus bar means, one of said means being interposed at an interruption of said power bus bar at each of said stations, said bus bar means being in alignment with respect to said power bus bar and insulated therefrom, control collector means carried by said conveyor and guided to engage said power bus bar substan tially continuously and to engage said interposed bus bar means sequentially as the collector means travel, a plurality of distinguishable trackside circuit means having circuit elements of differing reactive characteristics located ad? jacent said stop stations and electrically con-. nected to respective ones of said bus bar means, a plurality of trackside partial control circuits having circuit elements of difiering reactive characteristics located adjacent said track switch stations and. electrically connected to respective ones of said bus bar means, conveyor borne circuit means electrically connected to said collector means, said conveyor borne circuit means being manually adjustable as to its reactive characteristics to complete an electric control circuit resonant to a predetermined frequency of applied voltage only with the circuit means of a selected stop station, upon engagement of the collector means with the bus bar means of the selected station, means included in said control circuit and carried by said conveyor and operably responsive only to a resonant condition within said circuit to interrupt the flow of electric power to said propulsion motor at the selected stop station, a conveyor borne partial control circuit electrically connected to said collector means and manually adjustable as to its reactive character istics to complete an electric control circuit reso- 29 nant to a predetermined frequency of applied voltage only with the partial control circuit of a selected track switch station, upon engagement of the collector means with the bus bar means of the selected track switch station, and electric control means individual to said track switch stations and sequentially included in said lastmentioned control circuit and operably responsive only to a resonant condition within said control circuit to operate the corresponding track switch at the selected track switch station.

18. A trackway, a conveyor for travelling along said trackway, a power bus bar extending along said trackway, said power bus bar having a plurality of interruptions therein individual to said stations, a plurality of electrical connecting means located adjacent said stations and arranged substantially in alignment with and insulated from said power bus bar at said interruptions, a plurality of distinguishable trackside partial circuits having circuit elements of differing reactive characteristics located adjacent said stations and electrically connected to respective ones of said electrical connecting means, control collector means carried by said conveyor and guided to engage and cooperate with said power bus bar substantially continuously and to engage and cooperate with said electrical connecting means sequentially as the collector means travel, a conveyor borne partial circuit electrically connected to said collector means, said last-mentioned partial circuit being manually adjustable as to its reactive characteristics to complete a control circuit resonant to a predetermined frequency of applied voltage only with the partial circuit of a selected station, upon engagement of the collector means with the electrical connecting means of the selected station, and means included in said control circuit operably responsive only to a resonant condition within said circuit to control an operation atfecting the conveyor at the selected station.

19. A conveyor for travelling along a trackway, a power bus bar extending along said trackway, a plurality of spaced distinguishable selectee stations located alongside said trackway, said power bus bar having a plurality of interruptions therein individual to said stations, a plurality of electrical connecting means located adjacent said stations and arranged substantially in alignment with and insulated from said power bus bar at said interruptions, a plurality of distinguishable trackside partial circuits having circuit elements of differing reactive characteristics located adjacent said stations and electrically connected to respective ones of said electrical connecting means, control collector means carried by said conveyor and guided to engage and cooperate with said power bus bar substantially continuously and to engage and cooperate with said electrical connecting means sequentially as the collector means travel, a conveyor borne partial circuit electrically connected to said collector means, said last-mentioned partial circuit being manually adjustable as to its reactive characteristics to complete a control circuit resonant to a predetermined frequency of applied voltage only with the partial circuit of a selected station, upon engagement of the collector means with the electrical connecting means of the selected station, and means included in said control circuit operably responsive only to a resonant condition within said circuit to control an operation affecting the conveyor at the selected station.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,797,651 Gergacsevics et al. Mar. 24, 1931 1,797,864 Harlandt -l Mar. 24, 1931 1,817,692 Kloss et al Aug. 4, 1931 1,962,546 Woolley et al June 12, 1934 2,486,221 Spafiord Oct. 25, 1949 

